Input: evdev - indicate buffer overrun with SYN_DROPPED

  - Used to synchronize and separate touch events. See the

    multi-touch-protocol.txt document for more information.

* SYN_DROPPED:

  - Used to indicate buffer overrun in the evdev client's event queue.

    Client should ignore all events up to and including next SYN_REPORT

    event and query the device (using EVIOCG* ioctls) to obtain its

    current state.

EV_KEY:

----------

EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used

};

struct evdev_client {

	int head;

	int tail;

	unsigned int head;

	unsigned int tail;

	spinlock_t buffer_lock; /* protects access to buffer, head and tail */

	struct fasync_struct *fasync;

	struct evdev *evdev;

	struct list_head node;

	int bufsize;

	unsigned int bufsize;

	struct input_event buffer[];

};

static void evdev_pass_event(struct evdev_client *client,

			     struct input_event *event)

{

	/*

	 * Interrupts are disabled, just acquire the lock.

	 * Make sure we don't leave with the client buffer

	 * "empty" by having client->head == client->tail.

	 */

	/* Interrupts are disabled, just acquire the lock. */

	spin_lock(&client->buffer_lock);

	do {

	client->buffer[client->head++] = *event;

	client->head &= client->bufsize - 1;

	} while (client->head == client->tail);

	if (unlikely(client->head == client->tail)) {

		/*

		 * This effectively "drops" all unconsumed events, leaving

		 * EV_SYN/SYN_DROPPED plus the newest event in the queue.

		 */

		client->tail = (client->head - 2) & (client->bufsize - 1);

		client->buffer[client->tail].time = event->time;

		client->buffer[client->tail].type = EV_SYN;

		client->buffer[client->tail].code = SYN_DROPPED;

		client->buffer[client->tail].value = 0;

	}

	spin_unlock(&client->buffer_lock);

	if (event->type == EV_SYN)

#define SYN_REPORT		0

#define SYN_CONFIG		1

#define SYN_MT_REPORT		2

#define SYN_DROPPED		3

/*

 * Keys and buttons